Stress regulated semiconductor devices and associated methods

ABSTRACT

Stress regulated semiconductor devices and associated methods are provided. In one aspect, for example, a stress regulated semiconductor device can include a semiconductor layer, a stress regulating interface layer including a carbon layer formed on the semiconductor layer, and a heat spreader coupled to the carbon layer opposite the semiconductor layer. The stress regulating interface layer is operable to reduce the coefficient of thermal expansion difference between the semiconductor layer and the heat spreader to less than or equal to about 10 ppm/° C.

PRIORITY DATA

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/284,900, filed on Oct. 29, 2011, now U.S. Pat. No. 8,778,784which claims the benefit of U.S. Provisional Patent Application Ser. No.61/408,447, filed on Oct. 29, 2010, and which is a continuation-in-partof U.S. patent application Ser. No. 13/239,189, filed on Sep. 21, 2011,now U.S. Pat. No. 8,531,026 which claims the benefit of U.S. ProvisionalPatent Application Ser. Nos. 61/384,976 and 61/468,917, filed on Sep.21, 2010 and Mar. 29, 2011 respectively. This application is also acontinuation-in-part of U.S. patent application Ser. No. 13/344,527,filed on Jan. 5, 2012, now abandoned which claims the benefit of theTaiwan Patent Application Serial Number 100100357, filed on Jan. 5,2011. All of the aforementioned patent applications are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates generally to semiconductor devices andassociated methods. Accordingly, the present invention involves theelectrical and material science fields.

BACKGROUND OF THE INVENTION

In many developed countries, major portions of the populations considerelectronic devices to be integral to their lives. Such increasing useand dependence has generated a demand for electronics devices that aresmaller and faster. As electronic circuitry increases in speed anddecreases in size, cooling of such devices becomes problematic.

Electronic devices generally contain printed circuit boards havingintegrally connected electronic components that allow the overallfunctionality of the device. These electronic components, such asprocessors, transistors, resistors, capacitors, light-emitting diodes(LEDs), etc., generate significant amounts of heat. As it builds, heatcan cause various thermal problems associated with such electroniccomponents. Significant amounts of heat can affect the reliability of anelectronic device, or even cause it to fail by, for example, causingburn out or shorting both within the electronic components themselvesand across the surface of the printed circuit board. Thus, the buildupof heat can ultimately affect the functional life of the electronicdevice. This is particularly problematic for electronic components withhigh power and high current demands, as well as for the printed circuitboards that support them.

Various cooling devices have been employed such as fans, heat sinks,Peltier and liquid cooling devices, etc., as means of reducing heatbuildup in electronic devices. As increased speed and power consumptioncause increasing heat buildup, such cooling devices generally mustincrease in size to be effective and may also require power to operate.For example, fans must be increased in size and speed to increaseairflow, and heat sinks must be increased in size to increase heatcapacity and surface area. The demand for smaller electronic devices,however, not only precludes increasing the size of such cooling devices,but may also require a significant size decrease.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides stress regulatedsemiconductor devices and associated methods thereof. In one aspect, forexample, a stress regulated semiconductor device can include asemiconductor layer, a stress regulating interface layer including acarbon layer bonded to the semiconductor layer by a carbide former, anda heat spreader coupled to the stress regulating interface layeropposite the semiconductor layer. The stress regulating interface layeris operable to reduce the coefficient of thermal expansion differencebetween the semiconductor layer and the heat spreader to less than orequal to about 10 ppm/° C. In another aspect, the stress regulatinginterface layer is operable to reduce the coefficient of thermalexpansion difference between the semiconductor layer and the heatspreader to less than or equal to about 5 ppm/° C.

A variety of semiconductor materials are contemplated from which thedevices according to aspects of the present invention can beconstructed. In one aspect, nonlimiting examples of semiconductormaterials can include silicon, silicon carbide, silicon germanium,gallium arsenide, gallium nitride, germanium, zinc sulfide, galliumphosphide, gallium antimonide, gallium indium arsenide phosphide,aluminum phosphide, aluminum arsenide, aluminum gallium arsenide,gallium nitride, boron nitride, aluminum nitride, indium arsenide,indium phosphide, indium antimonide, indium nitride, and the like,including composites thereof. In one specific aspect, the semiconductormaterial can include gallium nitride, aluminum nitride, and compositesthereof.

Various carbon materials are also contemplated for inclusion in thecarbon layers according to aspects of the present invention. Nonlimitingexamples can include diamond-like carbon, boron-doped diamond, amorphousdiamond, crystalline diamond, polycrystalline diamond, graphite, and thelike, including combinations thereof. In one specific aspect, the carbonlayer has an amorphous atomic structure. In another specific aspect thecarbon layer is diamond-like carbon. In yet another specific aspect thecarbon layer is boron-doped diamond.

Various materials are contemplated for use in the heat spreader layersaccording to various aspects of the present invention. Nonlimitingexamples can include aluminum, copper, tin, tungsten, nickel, titanium,gold, silver, platinum, Al₂O₃, AlN, Si₃N₄, Si, glass, and combinationsand alloys thereof, and the like, including alloys and mixtures thereof.In one specific aspect the heat spreader includes copper.

In another aspect, a reflective layer disposed between the carbon layerand the semiconductor layer. In a more specific aspect, a carbide formerlayer can be disposed between the carbon layer and the reflective layer.In yet another aspect, a carbide former layer can be disposed betweenthe carbon layer and the heat spreader layer.

In another aspect of the present invention, a stress regulatedsemiconductor device is provided. Such a device can include asemiconductor layer and a heat spreader formed on the semiconductorlayer, where the heat spreader includes diamond particles uniformlydisposed within a metal matrix. The diamond particles are operable toreduce the coefficient of thermal expansion difference between thesemiconductor layer and the metal matrix to less than or equal to about10 ppm/° C. In another aspect, the diamond particles are operable toreduce the coefficient of thermal expansion difference between thesemiconductor layer and the metal matrix to less than or equal to about5 ppm/° C.

In yet another aspect of the present invention, a stress regulatedsemiconductor device is provided. Such a device can include asemiconductor layer, an electrically conductive boron nitride layerformed on the semiconductor layer, and a heat spreader coupled to theboron nitride layer opposite the semiconductor layer. The boron nitridelayer is operable to reduce the coefficient of thermal expansiondifference between the semiconductor layer and the heat spreader to lessthan or equal to about 10 ppm/° C.

In a further aspect of the present invention, a method for reducingstress induced defects in a semiconductor device is provided. Such amethod can include forming a stress regulating interface layer includinga carbon layer on a semiconductor layer, and coupling a heat spreaderlayer to the stress regulating interface layer opposite thesemiconductor layer. In some aspects, coupling the heat spreader to thestress regulating interface layer includes forming the heat spreader onthe stress regulating interface layer. The stress regulating interfacelayer reduces the coefficient of thermal expansion difference betweenthe semiconductor layer and the heat spreader to less than or equal toabout 10 ppm/° C. In another aspect, the method can further includeforming a reflective layer between the stress regulating interface layerand the semiconductor layer. In a more specific aspect, the method canfurther include forming a carbide former layer between the carbon layerand the reflective layer. In yet another aspect, the method can includeforming a carbide former layer between the carbon layer and the metalheat spreader layer.

In another aspect of the present invention, a stress regulatedlight-emitting semiconductor device is provided. Such a device caninclude a light-emitting semiconductor material, a carbon layer formedon the semiconductor material, and a metal heat spreader coupled to thecarbon layer, wherein the carbon layer is operable to reduce thecoefficient of thermal expansion difference between the semiconductorlayer and the metal heat spreader to less than or equal to about 10ppm/° C. In one aspect, the metal heat spreader is formed on the carbonlayer.

There has thus been outlined, rather broadly, various features of theinvention so that the detailed description thereof that follows may bebetter understood, and so that the present contribution to the art maybe better appreciated. Other features of the present invention willbecome clearer from the following detailed description of the invention,taken with the accompanying claims, or may be learned by the practice ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section view of a stress regulated semiconductordevice in accordance with one embodiment of the present invention.

FIG. 2 is a cross-section view of a stress regulated semiconductordevice in accordance with another embodiment of the present invention.

FIG. 3 is a cross-section view of a stress regulated semiconductordevice in accordance with yet another embodiment of the presentinvention.

FIG. 4 is a cross-section view of a stress regulated semiconductordevice in accordance with another embodiment of the present invention.

FIG. 5 is a cross-section view of a stress regulated semiconductordevice in accordance with yet another embodiment of the presentinvention.

FIG. 6 is a cross-section view of a stress regulated semiconductordevice in accordance with another embodiment of the present invention.

FIG. 7 is a cross-section view of a stress regulated semiconductordevice in accordance with another embodiment of the present invention.

FIG. 8 is a cross-section view of a stress regulated semiconductordevice in accordance with yet another embodiment of the presentinvention.

FIG. 9 is a cross-section view of a stress regulated semiconductordevice in accordance with another embodiment of the present invention.

FIG. 10 is a cross-section view of a stress regulated semiconductordevice in accordance with yet another embodiment of the presentinvention.

FIGS. 11A and B are SEM photos showing the peeling between plated metaland a semiconductive layer that can occur in a conventional LED;

FIG. 12 is a schematic view of an electron image of a vertical LED inaccordance with yet another embodiment of the present invention.

FIG. 13 shows data comparing the thermal expansion coefficient and thethermal conductivity coefficient of a diamond-Cu composite layer inaccordance with yet another embodiment of the present invention.

FIG. 14 provides data showing the CTE of a composite material as afunction of diamond vol % and Ti wt % in accordance with yet anotherembodiment of the present invention.

FIG. 15 provides data showing the CTE of a composite material as afunction of diamond size in accordance with yet another embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION Definitions

In describing and claiming the present invention, the followingterminology will be used in accordance with the definitions set forthbelow.

The singular forms “a,” “an,” and, “the” include plural referents unlessthe context clearly dictates otherwise. Thus, for example, reference to“a dopant” includes reference to one or more of such dopants, andreference to “the diamond layer” includes reference to one or more ofsuch layers.

As used herein, “vapor deposited” refers to materials which are formedusing vapor deposition techniques. “Vapor deposition” refers to aprocess of forming or depositing materials on a substrate through thevapor phase. Vapor deposition processes can include any process such as,but not limited to, chemical vapor deposition (CVD) and physical vapordeposition (PVD). A wide variety of variations of each vapor depositionmethod can be performed by those skilled in the art. Examples of vapordeposition methods include hot filament CVD, rf-CVD, laser CVD (LCVD),laser ablation, conformal diamond coating processes, metal-organic CVD(MOCVD), sputtering, thermal evaporation PVD, ionized metal PVD (IMPVD),electron beam PVD (EBPVD), reactive PVD, cathodic arc, and the like.

As used herein, “chemical vapor deposition,” or “CVD” refers to anymethod of chemically forming or depositing diamond particles in a vaporform upon a surface. Various CVD techniques are well known in the art.

As used herein, “physical vapor deposition,” or “PVD” refers to anymethod of physically forming or depositing diamond particles in a vaporform upon a surface. Various PVD techniques are well known in the art.

As used herein, “diamond” refers to a crystalline structure of carbonatoms bonded to other carbon atoms in a lattice of tetrahedralcoordination known as sp³ bonding. Specifically, each carbon atom issurrounded by and bonded to four other carbon atoms, each located on thetip of a regular tetrahedron. Further, the bond length between any twocarbon atoms is 1.54 angstroms at ambient temperature conditions, andthe angle between any two bonds is 109 degrees, 28 minutes, and 16seconds although experimental results may vary slightly. The structureand nature of diamond, including its physical and electrical propertiesare well known in the art.

As used herein, “distorted tetrahedral coordination” refers to atetrahedral bonding configuration of carbon atoms that is irregular, orhas deviated from the normal tetrahedron configuration of diamond asdescribed above. Such distortion generally results in lengthening ofsome bonds and shortening of others, as well as the variation of thebond angles between the bonds. Additionally, the distortion of thetetrahedron alters the characteristics and properties of the carbon toeffectively lie between the characteristics of carbon bonded in sp³configuration (i.e. diamond) and carbon bonded in sp² configuration(i.e. graphite). One example of material having carbon atoms bonded indistorted tetrahedral bonding is amorphous diamond.

As used herein, “diamond-like carbon” refers to a carbonaceous materialhaving carbon atoms as the majority element, with a substantial amountof such carbon atoms bonded in distorted tetrahedral coordination.Diamond-like carbon (DLC) can typically be formed by PVD processes,although CVD or other processes could be used such as vapor depositionprocesses. Notably, a variety of other elements can be included in theDLC material as either impurities, or as dopants, including withoutlimitation, hydrogen, sulfur, phosphorous, boron, nitrogen, silicon,tungsten, etc.

As used herein, “amorphous diamond” refers to a type of diamond-likecarbon having carbon atoms as the majority element, with a substantialamount of such carbon atoms bonded in distorted tetrahedralcoordination. In one aspect, the amount of carbon in the amorphousdiamond can be at least about 90%, with at least about 20% of suchcarbon being bonded in distorted tetrahedral coordination. Amorphousdiamond also has a higher atomic density than that of diamond (176atoms/cm³). Further, amorphous diamond and diamond materials contractupon melting.

The terms “heat transfer,” “heat movement,” and “heat transmission” canbe used interchangeably, and refer to the movement of heat from an areaof higher temperature to an area of cooler temperature. It is intendedthat the movement of heat include any mechanism of heat transmissionknown to one skilled in the art, such as, without limitation,conductive, convective, radiative, etc.

As used herein, “light-emitting surface” refers to a surface of a deviceor object from which light is intentionally emitted. Light may includevisible light and light within the ultraviolet spectrum. An example of alight-emitting surface may include, without limitation, a nitride layerof an LED, or of semiconductor layers to be incorporated into an LED,from which light is emitted.

As used herein, “substrate” refers to a support surface to which variousmaterials can be joined in forming a semiconductor orsemiconductor-on-diamond device. The substrate may be any shape,thickness, or material, required in order to achieve a specific result,and includes but is not limited to metals, alloys, ceramics, andmixtures thereof. Further, in some aspects, the substrate may be anexisting semiconductor device or wafer, or may be a material which iscapable of being joined to a suitable device.

As used herein, the term “substantially” refers to the complete ornearly complete extent or degree of an action, characteristic, property,state, structure, item, or result. For example, an object that is“substantially” enclosed would mean that the object is either completelyenclosed or nearly completely enclosed. The exact allowable degree ofdeviation from absolute completeness may in some cases depend on thespecific context. However, generally speaking the nearness of completionwill be so as to have the same overall result as if absolute and totalcompletion were obtained. The use of “substantially” is equallyapplicable when used in a negative connotation to refer to the completeor near complete lack of an action, characteristic, property, state,structure, item, or result. For example, a composition that is“substantially free of” particles would either completely lackparticles, or so nearly completely lack particles that the effect wouldbe the same as if it completely lacked particles. In other words, acomposition that is “substantially free of” an ingredient or element maystill actually contain such item as long as there is no measurableeffect thereof.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 1 to about 5” should beinterpreted to include not only the explicitly recited values of about 1to about 5, but also include individual values and sub-ranges within theindicated range. Thus, included in this numerical range are individualvalues such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4,and from 3-5, etc., as well as 1, 2, 3, 4, and 5, individually.

This same principle applies to ranges reciting only one numerical valueas a minimum or a maximum. Furthermore, such an interpretation shouldapply regardless of the breadth of the range or the characteristicsbeing described.

The Invention

The present invention provides stress regulated semiconductor devicesand methods associated therewith. Such devices can provide moreeffective cooling than traditional devices, and as such can be operatedat a higher operational power. In one aspect, a vertical design for asemiconductor device can be utilized. One example of a vertical designsemiconductor is a vertical stack LED. Much of the following discussionis directed to vertical stack LED devices for convenience. It is notedthat this is for convenience sake, and that any type of semiconductordevice and/or semiconductor configuration or design is considered to bewithin the present scope.

One potential technique for cooling a vertical stack LED is the use of acopper coated wafer to provide an integrated heat spreader that isintimately in contact with the semiconductor material. One problem,however, exists due to the difference in the coefficient of thermalexpansion (CTE) between copper and many semiconductor materials. Therecan be a 3 times difference in the CTE of copper compared to asemiconductor material such as silicon. When such an LED is operated athigh temperature, the copper expands and contracts to a much greaterextent than semiconductor materials for a given temperature change, andcan result in microcracks, delamination, and other defects at theinterface between the copper and the semiconductor materials. Thesemicrocracks can lead to LED failure over time.

In addition to operational failures, in some cases defects can beintroduced into a semiconductor device during the manufacturing process.For example, one technique of manufacturing may be to couple a metalheat spreader to a semiconductor material by soldering. Thermal mismatchbetween these materials during soldering can cause defects, cracking,delamination, and the like to occur or begin to occur.

The inventors have discovered that various materials can be used tomoderate the CTE mismatch between a heat spreading material such ascopper and a semiconductor, and thus decrease the interface stress therebetween due to temperature cycling during manufacture and/or use. Suchmaterials can include, without limitation, various forms of diamond,graphite, boron nitrides, and the like. As an additional advantage,these materials tend to be good thermal conductors, and thus facilitatethe movement of heat from the semiconductor. Much of the followingdiscussion is directed to diamond materials for convenience, and it isnoted that any material capable of moderating the CTE between disparatematerials should be considered to be within the present scope.

Semiconductor devices according to aspects of the present invention canbe utilized in a variety of applications, including LEDs, laser diodes,p-n junction devices, p-i-n junction devices, SAW and BAW filters, andthe like. In one aspect, the semiconductor device is an LED device. Inone specific aspect, the semiconductor device is an LED device with avertical stack configuration.

In one aspect, as is shown in FIG. 1, a stress regulated semiconductordevice 10 can include a semiconductor layer 12, a carbon layer 14 formedon the semiconductor layer 12, and a heat spreader 16 coupled to thecarbon layer 14 opposite the semiconductor layer 12. The carbon layer 14is operable to reduce the CTE difference between the semiconductor layer12 and the heat spreader 16 to less than or equal to about 10 ppm/° C.In another aspect, the carbon layer is operable to reduce the CTEdifference between the semiconductor layer and the heat spreader to lessthan or equal to about 5 ppm/° C. Additionally, the carbon layer can beconductive, non-conductive, or semiconductive, depending on the designof the device. It should be noted that in FIG. 1 and all followingFIGs., the semiconductor layer 12 can be one or more layers, junctions,structures, and the like.

The carbon layer can be a single carbon layer or multiple carbon layers,and can include other materials or material layers such as, for example,carbide formers. The term “stress regulating interface layer” can beused to describe one or more carbon layers and any associated materialsor material layers therewith. For example, in one aspect a stressregulating interface layer can include a carbon layer and a carbideformer.

One benefit of the vertical stack design relates to the placement ofelectrical contacts in association with the semiconductor. As opposed tomore traditional designs, electrical contacts in a vertical stack LEDare located on opposite sides of the semiconductor from one another.This allows a linear flow of current from one electrical contact to theother. As is shown in FIG. 2, for example, a vertical stack device 20can include a semiconductor layer 12, a carbon layer 14 formed on thesemiconductor layer, and a heat spreader layer 16 formed on the carbonlayer opposite the semiconductor layer. In addition, an electricalcontact 18 can be coupled to the semiconductor layer on an opposite sidefrom the heat spreader layer 16. In this case, the carbon layer isconductive to allow the carbon layer and/or the heat spreader layer toact as the other electrical contact. Thus, electrical current flowslinearly from one electrical contact to the other. It should be notedthat, in some aspects, a second electrical contact in addition to thecarbon layer and/or the heat spreader layer can be coupled to thedevice.

Various additional layers are also contemplated for inclusion in devicesaccording to aspects of the present invention. For example, for manyapplications, including light-generating devices, it can be beneficialto include a reflective layer positioned to focus and/or direct light.As one example, as is shown in FIG. 3, an LED device 30 can include areflective layer 32 disposed between the carbon layer 14 and thesemiconductor layer 12. Light generated in the semiconductor layer ofthe vertical stack LED device can be transmitted in multiple directions.One portion of the light can be transmitted forward through thesemiconductor layer 12 and out of the device in a direction away fromthe heat spreader layer 16. Another portion can be transmitted from thesemiconductor layer 12 toward the heat spreader layer 16 and the carbonlayer 14. Thus the reflective layer 32 can function to reflect at leasta portion of this light back through the semiconductor layer and out ofthe LED, thus increasing the light output of the device. Depending onthe optical properties of the particular diamond layer used, thereflective layer can be disposed between the semiconductor layer and thecarbon layer as shown, or it can be disposed between the carbon layerand the heat spreader layer (not shown).

In some aspects, it can be beneficial to provide an interlayer betweenthe carbon layer and another layer that the carbon layer is bonded to.For example, a carbide former layer can improve the bonding between acarbon material such as diamond and a variety of other materials. As isshown in FIG. 4, for example, a carbide former layer 42 (i.e.interlayer) can be disposed between the carbon layer 14 and thereflective layer 32 in order to improve the coupling of the carbon layerto the reflective layer. In another aspect, as is shown in FIG. 5, acarbide former layer 42 can be disposed between the carbon layer 14 andthe heat spreader layer 16 in order to improve the coupling of the heatspreader layer to the carbon layer. A carbide former layer can also beutilized between a carbon layer and a semiconductor layer (not shown).

Additionally, the CTE mismatch can be further moderated by utilizingmultiple carbon layers. Furthermore, in some aspects it can bebeneficial to alternate additional layers in between multiple carbonlayers. For example, in one aspect a stack of multiple carbon layers caninclude carbide former layers interspersed between the carbon layers. Inone specific aspect, a stress regulating interface layer can includemultiple carbon layers having titanium layers interspersed therebetweento provide improved CTE matching between the heat spreader and thesemiconductor layer. In one specific aspect, a stress regulatinginterface layer can include alternating layers of DLC and a carbideformer such as Ti to improve CTE matching.

In addition to diamond layers, diamond particles 64 can also be utilizedto reduce the CTE mismatch between the metal heat spreader and thesemiconductor layer. As is shown in FIG. 6, for example, a stressregulated semiconductor device 60 can include a semiconductor layer 12and a heat spreader layer 62 formed on the semiconductor layer 12.Diamond particles 64 are uniformly disposed within the metal heatspreader layer 62. The presence of the diamond particles can reduce theCTE mismatch between the semiconductor layer and the heat spreaderlayer. As is shown in FIG. 7, the diamond particles 64 can also bearranged in a monolayer. In one aspect, the diamond particles areoperable to reduce the CTE difference between the semiconductor layerand the metal matrix to less than or equal to about 10 ppm/° C. Inanother aspect, the diamond particles are operable to reduce the CTEdifference between the semiconductor layer and the metal matrix to lessthan or equal to about 5 ppm/° C. It can be beneficial to form the heatspreader layer including the diamond particles on the semiconductorlayer during manufacture of the semiconductor device, as opposed tomaking a diamond monolayer/metal heat spreader device separately forlater attachment, as the soldering step is avoided.

In another aspect of the present invention, a stress regulatedsemiconductor device can be made according to the following method. Asis shown in FIG. 8, a carbon layer 82 is formed on a semiconductor layer84 having a substrate 86 such as sapphire. In one specific aspect, thesemiconductor layer can include GaN. In some aspects, a carbide formerlayer can be deposited between the carbon layer 82 and the semiconductorlayer 84 to improve bonding as has been described (not shown). As isshown in FIG. 9, a heat spreader layer 92 is formed on the carbon layer82. In some aspects, a carbide former layer can be deposited on thecarbon layer 82 to improve bonding with the heat spreader layer 92 ashas been described (not shown). Additionally, the heat spreader layercan be thickened to improve the thermal conductivity and/or physicalstability of the device. The substrate 86 can be removed as is shown inFIG. 10, and in some aspects, subsequent semiconductive structures canbe deposited on the exposed surface of the semiconductor layer 84. Thesubstrate can be removed by a variety of known methods, including lasersplitting, mechanical removal, chemical etching, and the like. In someaspects, the exposed surface of the semiconductor layer can be leveledor planarized to improve subsequent deposition thereupon. Note that thedevice is shown rotated 180° in FIG. 10 for clarity.

It should be noted that in aspects of the present disclosure, at least afirst and a second electrode can be coupled to the LED. In one aspect,for example, a first electrode can be coupled to one side of thesemiconductor layer opposite the diamond-like carbon layer, and a secondelectrode can be coupled to the heat spreader side of the LED. In someaspects, a metal heat spreader can be utilized as an electrode.

In another aspect of the present invention, a method for reducing stressinduced defects in a semiconductor device is provided. Such a method caninclude forming a diamond layer on a semiconductor layer and coupling aheat spreader layer to the diamond layer opposite the semiconductorlayer. The diamond layer reduces the coefficient of thermal expansiondifference between the semiconductor layer and the heat spreader to lessthan or equal to about 10 ppm/° C. In one aspect, the method canadditionally include forming a reflective layer between the diamondlayer and the semiconductor layer. As has been described, in someaspects a carbide former layer can be formed between the diamond layerand the reflective layer. In other aspects, a carbide former layer canbe formed between the diamond layer and the heat spreader layer. In yetanother aspect, coupling the heat spreader to the diamond layer includesforming the heat spreader on the diamond layer.

Numerous types of carbon materials are contemplated for use as carbonlayers according to aspects of the present invention. Non-limitingexamples include amorphous diamond, diamond-like carbon, polycrystallinediamond, crystalline diamond, single crystal diamond, graphite, and thelike. In one aspect, the carbon layer can be an amorphous diamond layer.In another aspect, the carbon layer can be a diamond-like carbon layer.It should be noted that any type of carbon layer can be utilizedprovided the layer can be formed on a semiconductor layer.

In one aspect, improved CTE matching can be achieved by utilizing astress regulating interface layer having a carbon layer with anamorphous atomic structure. Examples of such amorphous materials caninclude diamond-like carbon, amorphous diamond, and the like. Withoutintending to be bound by any scientific theory, amorphous materials suchas diamond-like carbon have a high elastic or yield limit due to theirnon-crystalline structure. Thus when disposed between two rigidstructures such as a heat spreader and a semiconductor during heatingand cooling, the amorphous structure of materials such as diamond-likecarbon can absorb the expansion and contraction differences betweenthese materials as they expand and contract at different rates.

The carbon layers according to aspects of the present invention can beof any thickness that would allow thermal cooling and CTE mismatchmoderation of a semiconductor device. Thicknesses can vary depending onthe application and the semiconductor device configuration. For example,greater cooling requirements may require thicker carbon layers. Thethickness may also vary depending on the material used in the carbonlayer. In some aspects, particularly those where the thickness of thedevice is to be minimized, it can be beneficial to utilize a carbonlayer that is no thicker than necessary for the application. That beingsaid, in one aspect a carbon layer may be from about 10 microns to about300 microns thick. In another aspect, a carbon layer may be less than orequal to about 10 microns thick. In yet another aspect, a carbon layermay be from about 50 microns to about 100 microns thick. In a furtheraspect, a carbon layer may be greater than about 50 microns thick. Inyet another aspect, the carbon layer can be from about 1 micron to about30 microns thick. In a further aspect, the carbon layer can be fromabout 5 microns to about 30 microns thick. In yet a further aspect, thecarbon layer can be less than about 1 micron thick. In one aspect, thecarbon layer can be from about 0.1 microns to about 10 microns thick. Inanother aspect, the carbon layer can be from about 0.5 microns to about2 microns thick. In yet another aspect, the carbon layer can be at leastabout 300 nm thick. In another aspect, the carbon layer can be at leastabout 500 nm thick.

In one aspect, the carbon layer can be a diamond material such as, forexample, crystalline diamond, amorphous diamond, diamond-like carbon,and the like. Diamond materials have excellent thermal conductivityproperties that make them ideal for incorporation into semiconductordevices as has been described herein. The transfer of heat that ispresent in the semiconductor device can thus be accelerated from thedevice through a diamond material. It should be noted that the presentinvention is not limited as to specific theories of heat transmission.As such, in one aspect the accelerated movement of heat from inside thedevice can be at least partially due to heat movement into and through adiamond layer. Due to the heat conductive properties of diamond, heatcan rapidly spread laterally through the diamond layer and to the edgesof a semiconductor device. Heat present around the edges will be morerapidly dissipated into the air or into surrounding structures, such asheat spreaders or device supports. Additionally, the diamond layer canthermally conduct heat to the metal heat spreader layer that isintimately contacted therewith. Because the thermal conductivity ofdiamond is greater than the thermal conductivity of a semiconductorlayer to which it is thermally coupled, a heat sink is established bythe diamond layer. Thus heat that builds up in the semiconductor layeris drawn into the diamond layer and spread laterally to be transferredinto the metal heat spreader. Such accelerated heat transfer can resultin semiconductor devices with much cooler operational temperatures.Additionally, the acceleration of heat transfer not only cools asemiconductor device, but may also reduce the heat load on manyelectronic components that are spatially located nearby thesemiconductor device.

It should be understood that the following is a very general discussionof diamond deposition techniques that may or may not apply to aparticular layer or application, and that such techniques may varywidely between the various aspects of the present invention.Additionally, and as has been noted, other materials such as boronnitride and graphite are included within the present scope. Thefollowing deposition techniques should also be applied to thosematerials where applicable. Generally, diamond layers may be formed byany means known, including various vapor deposition techniques. Anynumber of known vapor deposition techniques may be used to form thesediamond layers. Common vapor deposition techniques include chemicalvapor deposition (CVD) and physical vapor deposition (PVD), although anysimilar method can be used if similar properties and results areobtained. In one aspect, CVD techniques such as hot filament, microwaveplasma, oxyacetylene flame, rf-CVD, laser CVD (LCVD), metal-organic CVD(MOCVD), laser ablation, conformal diamond coating processes, and directcurrent arc techniques may be utilized. Typical CVD techniques use gasreactants to deposit the diamond or diamond-like material in a layer, orfilm. These gases generally include a small amount (i.e. less than about5%) of a carbonaceous material, such as methane, diluted in hydrogen. Avariety of specific CVD processes, including equipment and conditions,as well as those used for semiconductor layers, are well known to thoseskilled in the art. In another aspect, PVD techniques such assputtering, cathodic arc, and thermal evaporation may be utilized.Additionally, molecular beam epitaxy (MBE), atomic layer deposition(ALD), and the like can additionally be used. Further, specificdeposition conditions may be used in order to adjust the exact type ofmaterial to be deposited, whether DLC, amorphous diamond, or purediamond.

In some aspects a nucleation enhancer layer or carbide former layer canbe formed on the growth surface of a substrate in order to improve thequality and deposition time of the diamond layer. As has been described,the diamond layer can be deposited on various material layers, such as asemiconductor layer or reflective layer. In one aspect, a diamond layercan be formed by depositing applicable nuclei, such as diamond nuclei,on a diamond growth surface of a substrate and then growing the nucleiinto a film or layer using a vapor deposition technique. In one aspectof the present invention, a nucleation enhancer layer can be coated uponthe substrate to enhance the growth of the diamond layer. Diamond nucleiare then placed upon the nucleation enhancer layer, and the growth ofthe diamond layer proceeds via CVD.

A variety of suitable materials will be recognized by those in skilledin the art which can serve as a nucleation enhancer. In one aspect ofthe present invention, the nucleation enhancer may be a materialselected from the group consisting of metals, metal alloys, metalcompounds, carbides, carbide formers, and mixtures thereof. In anotheraspect, the nucleation enhancer layer can be a carbide former layerincluding a carbide former material. Examples of carbide formermaterials may include, without limitation, tungsten (W), tantalum (Ta),titanium (Ti), zirconium (Zr), chromium (Cr), molybdenum (Mo), silicon(Si), manganese (Mn), vanadium (V), niobium (Nb), hafnium (Hf), and thelike, including combinations thereof. Additionally, examples of carbidesinclude tungsten carbide (WC), silicon carbide (SiC), titanium carbide(TiC), zirconium carbide (ZrC), and mixtures thereof among others. Inone specific aspect, the carbide former layer can be Ti. In anotherspecific aspect, the carbide former layer can be Cr. It should be notedthat a carbide former layer can be utilized to enhance the deposition ofa diamond layer, a carbon layer, a boron nitride layer, or an additionalmaterial such as a heat spreader material upon one or more of theaforementioned layers. Additionally, a carbide former layer can beutilized to improve bonding between layers, and many not necessarilyinvolve enhanced nucleation in all cases. In one specific aspect, usefulcarbide formers can include Ti, W, TiW, Cr, Pt, Zr, V, and the like.

A nucleation enhancer layer or a carbide former layer, when used, is alayer that is thin enough that it does not to adversely affect thethermal transmission properties of the device. In one aspect, thethickness of these layers may be less than about 0.5 micrometers. Inanother aspect, the thickness may be less than about 10 nanometers. Inyet another aspect, the thickness is less than about 5 nanometers. In afurther aspect of the invention, the thickness is less than about 3nanometers. In one aspect, the thickness is from about 50 nm to about500 nm. In yet another aspect, the thickness is about 100 nm.

Diamond materials having higher proportions of sp3 bonds have higherthermal conductivity while moderating CTE mismatch between the heatspreader and the semiconductor layer. Various methods may be employedthat can affect the sp3 content of the diamond in the diamond layer thatis created by vapor deposition techniques. For example, reducing themethane flow rate and increasing the total gas pressure during the earlyphase of diamond deposition can decrease the decomposition rate ofcarbon, and increase the concentration of hydrogen atoms. Thus asignificantly higher percentage of the carbon will be deposited in a sp³bonding configuration, and thus the quality of the diamond nuclei formedcan be increased. Additionally, the nucleation rate of diamond particlesdeposited on a growth surface of the substrate or the nucleationenhancer layer can be increased in order to reduce the amount ofinterstitial space between growing diamond particles. Examples of waysto increase nucleation rates include, but are not limited to; applying anegative bias in an appropriate amount, often about 100 volts, to thegrowth surface; polishing the growth surface with a fine diamond pasteor powder, which may partially remain on the growth surface; andcontrolling the composition of the growth surface such as by ionimplantation of C, Si, Cr, Mn, Ti, V, Zr, W, Mo, Ta, and the like by PVDor PECVD. PVD processes are typically at lower temperatures than CVDprocesses and in some cases can be below about 250° C. such as about150° C. Other methods of increasing diamond nucleation will be readilyapparent to those skilled in the art.

In one aspect of the present invention, the carbon layer may be formedas a conformal diamond layer. Conformal diamond coating processes canprovide a number of advantages over conventional diamond film processes.Conformal diamond coating can be performed on a wide variety ofsubstrates, including non-planar substrates. A growth surface can bepretreated under diamond growth conditions in the absence of a bias toform a carbon film. The diamond growth conditions can be conditions thatare conventional CVD deposition conditions for diamond without anapplied bias. As a result, a thin carbon film can be formed which istypically less than about 100 angstroms. The pretreatment step can beperformed at almost any growth temperature such as from about 200° C. toabout 900° C., although lower temperatures below about 500° C. may bepreferred. Without being bound to any particular theory, the thin carbonfilm appears to form within a short time, e.g., less than one hour, andis a hydrogen terminated amorphous diamond.

Following formation of the thin carbon film, the growth surface may thenbe subjected to diamond growth conditions to form a conformal diamondlayer. The diamond growth conditions may be those conditions which arecommonly used in traditional CVD diamond growth. However, unlikeconventional diamond film growth, the diamond film produced using theabove pretreatment steps results in a conformal diamond film thattypically begins growth substantially over the entire growth surfacewith substantially no incubation time. In addition, a continuous film,e.g. substantially no grain boundaries, can develop within about 80 nmof growth. Diamond layers having substantially no grain boundaries maymove heat more efficiently than those layers having grain boundaries.

Additionally, in some aspects the carbon layer can be a conductivecarbon layer such as a conductive diamond layer. Various techniques maybe employed to render a diamond layer conductive. Such techniques areknown to those of ordinary skill in the art. For example, variousimpurities may be doped into the crystal lattice of the diamond layer.Such impurities may include elements such as Si, B, P, N, Li, Al, Ga,etc. In one specific aspect, for example, the diamond layer may be dopedwith B. Impurities may also include metallic particles within thecrystal lattice, provided they do not interfere with the function of thedevice, such as by blocking light emitted from an LED.

Various semiconductor materials are contemplated that can be used in thedevices of the present invention. The semiconductor layer may includeany material that is suitable for forming electronic devices,semiconductor devices, or the like. Many semiconductors are based onsilicon, gallium, indium, and germanium. Suitable materials for thesemiconductor layer can include, without limitation, silicon, siliconcarbide, silicon germanium, gallium arsenide, gallium nitride,germanium, zinc sulfide, gallium phosphide, gallium antimonide, galliumindium arsenide phosphide, aluminum phosphide, aluminum arsenide,aluminum gallium arsenide, gallium nitride, boron nitride, aluminumnitride, indium arsenide, indium phosphide, indium antimonide, indiumnitride, indium gallium nitride, and composites thereof. In one aspect,however, the semiconductor layer can include silicon, silicon carbide,gallium arsenide, gallium nitride, gallium phosphide, aluminum nitride,indium nitride, indium gallium nitride, aluminum gallium nitride, orcomposites of these materials. In one specific aspect, the semiconductormaterial includes gallium nitride. In another specific aspect, thesemiconductor material includes aluminum nitride. In yet another aspect,the semiconductor material includes indium nitride. In a further aspect,the semiconductor includes (Al, Ga, In)N. In yet another aspect, thesemiconductor material can include elements selected from Group IIelements to Group VI elements.

Additionally, semiconductor materials may be of any structuralconfiguration known, for example, without limitation, cubic (zincblendeor sphalerite), wurtzitic, rhombohedral, graphitic, turbostratic,pyrolytic, hexagonal, amorphous, or combinations thereof. As such, thesemiconductor layer can be formed by any method known to one of ordinaryskill in the art. Various known methods of vapor deposition can beutilized, as has been described. Additionally, surface processing may beperformed between any of the deposition steps described in order toprovide a smooth surface for subsequent deposition. Such processing maybe accomplished by any means known, such as by chemical etching,polishing, buffing, grinding, etc.

Various materials are contemplated for use as a substrate upon which thesemiconductor layer can be deposited. Any material that is suitable forthis purpose is considered to be within the present scope. Non-limitingexamples of such materials include Al₂O₃, Si, SiC, GaAs, GaP, AlP, GaN,graphite, hBN, or diamond. Other examples can include a nitride, aphosphide, or an arsenide including at least one cation such as B, Al,Ga, In, Be, or Mg.

The reflective layer can be made from a variety of reflective materials.Non-limiting examples include Ag, Al, Ni, Co, Pd, Pt, Au, Zn, Sn, Sb,Pb, Cu, CuAg, NiAg, and alloys thereof. The thickness of the reflectivelayer is not specifically limited, as long as the purpose for lightguiding can be realized and the light-illumination efficiency can beincreased. In one aspect, the thickness of the reflective layer can befrom about 100 nm to about 500 nm. In another aspect, the thickness canbe about 200 nm.

Various materials are contemplated for use in the heat spreader layer.Any material that can be utilized in the devices according to aspects ofthe present invention are considered to be within the present scope.Nonlimiting examples of such materials can include aluminum, copper,tin, tungsten, nickel, titanium, gold, silver, platinum, Al₂O₃, AlN,Si₃N₄, Si, glass, and combinations and alloys thereof, and the like,including mixtures and alloys thereof. In one aspect, the heat spreadercan be a metal heat spreader. In one specific aspect, the heat spreaderincludes copper. Additionally, the heat spreader materials can beapplied to the device using any deposition technique. In one aspect, forexample, the material can be deposited by sputtering. In another aspect,the heat spreader can be soldered to the device using, for example, Auor Au—Sn.

Additionally, in some aspects the heat spreader can be a compositematerial of a metal and diamond particles. In one aspect, the diamondscan be arranged in only a single layer within the metal material. Inanother aspect, the diamonds can be arranged in multiple single layersthroughout the metal material. In yet another aspect, the diamonds canbe arranged in more of a randomly distributed pattern throughout themetal. In one aspect, the content of the diamond particles in thecomposite material can be from about 25 wt % to about 60 wt %. Inanother aspect, the content of the diamond particles in the compositematerial can be from about 30% to about 50%. Furthermore, while avariety of metals are contemplated, non-limiting examples include atleast one of Cu, Ag, Co, Ni, W, Fe, Ti, Cr, B, and the like, includingcombinations thereof. The diamond can be natural or synthetic diamondparticles. Furthermore, in one aspect the diameter of the diamond can befrom about 1 μm to about 1 mm. In one specific aspect, the compositematerial includes diamond particle impregnated nickel.

The thickness of the composite material is not specially limited, andany useful thickness is considered to be within the present scope. Inone aspect, for example, the thickness of the composite material layercan be from about 100 μm to about 500 μm. In another aspect, the layercan be about 150 μm thick. The thermal expansion coefficient of thecomposite material layer can be properly adjusted according to the needsof a given situation so as to avoid bending or causing an internaldefect of the LED due to interfacial stress, which may reduce the yield,increase the manufacturing cost, and increase light attenuation.Accordingly, in one aspect the thermal expansion coefficient of thecomposite material layer can be from about 2 ppm/° C. to about 10 ppm/°C.

Further, in some aspects, the composite material layer can be polishedto an Ra of less than about 1 μm, so as to keep the flatness of theremaining surface to under ±1 mm. The same is polishing can be performedon any type of layer in the LED, including a heat spreader layer.

Following deposition of the heat spreader layer, the thickness of thelayer can be increased via a thickening process. Such thickening canincrease the thermal conductivity of the device, provide for additionalstructural support for the semiconductor materials, facilitate devicehandling and attachment to other substrates, and the like. As oneexample, a temporary support substrate can be removed from thesemiconductor device once the heat spreader layer has been increased toa thickness that is capable of providing adequate support. As such, inone aspect a heat spreader has a minimum thickness for supporting thesemiconductor material such that bowing does not occur. Although anymethod of thickening is contemplated, in one aspect a metal heatspreader can be thickened by further sputtering of the heat spreadermaterial and/or an additional metal material. In another aspect, themetal heat spreader layer can be thickened by electroplating additionalmetal material thereupon. The metal material can be the same ordifferent from the metal material originally sputtered onto the device.In some aspects, a monolayer of diamond particles can be disposed on thesputtered metal heat spreader layer. Subsequent electroplating willthicken the metal heat spreader layer, thus incorporating the diamondparticles within the metal material.

In another aspect of the present disclosure, a transparent diamond-likecarbon layer can be formed on one side of the semiconductive layer, soas to dissipate heat generated from the phosphor layer of the LED, andincrease the light-emitting efficiency and lifetime of the LED. Forexample, the transparent diamond-like carbon layer can be formed on theside of the semiconductor layer opposite the diamond-like carbon layer,or in other words, on the side opposite from the heat spreader. Thetransparent diamond like carbon layer can be formed by any depositionmethod, such as, for example, a plasma chemical vapor deposition (PECVD)method. One way of forming a diamond-like carbon layer that istransparent is to include hydrogen atoms in the deposited layer. In oneaspect, the content of the hydrogen atoms can be from about 15 at % toabout 40 at % based on the total amount of the transparent diamond likecarbon layer, so as to increase the heat-dissipating rate and lightemitting efficiency.

According to a conventional LED designs, the positive and the negativeelectrodes are located on the same side to the semiconductive layer. Dueto the dielectric nature of common sapphire substrates, electricalcurrent generated by the semiconductive layer flows vertically down andthen turns to flow horizontally. As a result, a current accumulationoccurs at the inner corner of the semiconductive layer, so as to hinderthe electron layer and the hole layer of the P—N surface. This can causethe illumination efficiency to decrease. A hot point is also generatedwhen current accumulation occurs in the semiconductive layer, which maycause a defect to the crystalline of the semiconductive layer and reducethe lifespan of the LED. Since the thermal expansion coefficient of themetallic reflective layer is greater than that of a semiconductive layersuch as GaN, stress can incur at the interface. Therefore, for aconventional LED, an electrical current may proceed along the path withminimum resistance while electrified, and a portion having greaterstress may result in rising temperature, so as the crystal lattice canbe expanded by the metallic reflective layer. As shown in FIGS. 11A and11B, particularly with a high frequency of turning on and off the LED,defects can be induced by the repeated movements of the crystal latticeof the semiconductive layer, which results in a rapid decrease of thebrightness of the LED.

In contrast, for the vertical LED of the present disclosure, heatgenerated by the LED during illumination can be dissipated/conductedaway rapidly due to the diamond-like carbon layer and/or thediamond-containing heat spreader having a high thermal conductivity, andthus can avoid problems such as light attenuation and short lifespan dueto defects of the crystalline semiconductor material caused by thenon-uniformity of the inner electrical current. Since the stress at theinterface is extensively reduced, problems such as light attenuation andshort lifespan due to defects of the crystalline lattice caused by thenon-uniformity of the inner electrical current can be avoided, as shownin FIG. 12.

As a result, the current vertical LED allows the realization of lightemitting diodes of a large scale (>1 mm), a large current (>1 A/mm2),and a large power (>10 W), which cannot be achieved by conventionallight emitting diodes having a curving current therein. Furthermore, thevertical LED of the present disclosure has advantages of high luminance,high brightness, high heat-dissipation rate (due to the excellent heatconductivity of the diamond-like carbon layer) during illumination, andfreedom from internal defects, so as to realize a long lifetime.

Furthermore, as for the composite material layer (i.e. the heatspreader) and the diamond-like carbon layer in the present invention,analysis results show that the thermal expansion coefficient of thepresent LED is properly controlled, and the thermal resistance isreduced (See FIG. 13). As has been described, the coefficient of thermalexpansion (CTE) can be adjusted depending on the diameter and the volumepercentage of the diamond in a heat spreader composite material. Inorder to obtain a good coefficient of thermal expansion (e.g. about 2-10ppm/° C.), the volume percentage of the diamond is can be about 30-50Vol %, as shown in FIG. 14, and the diameter of the diamond can be as isshown in FIG. 15.

Therefore, according to the LED provided by the method of the presentexample, a light emitting diode of large scale (>1 mm), large current(>1 A/mm2), and large power (>10 W) can be realized, which cannot beobtained by parallel connection of plural conventional light emittingdiodes that have a curving current therein. Furthermore, the verticallight emitting diode and/or the method of fabricating the same of thepresent example have advantages of high luminance, high brightness, highheat-dissipation rate (due to the excellent heat conductivity of thediamond-like carbon layer) during illumination, and free of internaldefects so as to realize a long lifetime, which cannot be obtained by aconventional light emitting diode.

EXAMPLES

The following examples illustrate various techniques of makingsemiconductor devices according to aspects of the present invention.However, it is to be understood that the following are only exemplary orillustrative of the application of the principles of the presentinvention. Numerous modifications and alternative compositions, methods,and systems can be devised by those skilled in the art without departingfrom the spirit and scope of the present invention. The appended claimsare intended to cover such modifications and arrangements. Thus, whilethe present invention has been described above with particularity, thefollowing Examples provide further detail in connection with severalspecific embodiments of the invention.

Example 1

A 2 inch sapphire wafer is deposited with epitaxial GaN by MOCVD (metalorganic chemical vapor deposition). Trimethylgallium is used as the Gasource gas and ammonia is added to supply nitrogen atoms. Hydrogen isalso added in order to dilute the gas and to gasify Ga or N atoms ifthey are located in unstable sites on the lattice. A multiple layeredsemiconductor structure is made by n-doping with Si on the sapphirefollowed by p-doping with Mg to form a junction. Quantum wells andintrinsic layers can be introduced between the p-doped layer and then-doped layer. The top surface of the p-doped layer is sputtered with areflective layer of Ag to a thickness of about 200 nm. The reflectivelayer is then sputtered with a nucleation enhancing layer of Ti to about50 nm thick.

Subsequently, amorphous diamond is deposited on the nucleation enhancinglayer to a thickness of about 1 μm by cathodic arc deposition. Anadditional nucleation enhancing layer of Ti is sputtered on theamorphous diamond layer to a thickness of about 50 nm, followed bysputtering of a Cu metal layer. The device is then removed from thedeposition chamber and immersed in an electrolyte solution where the Culayer is thickened by electroplating. A region of the GaN layer is thenlaser irradiated to separate the sapphire wafer from the GaN layer. Thenewly exposed n-doped GaN surface is then sputtered with Au as electrodeat one corner. This will form a vertical stack LED with top and bottomelectrodes.

Example 2

A 2 inch sapphire wafer is deposited with epitaxial GaN by MOCVD (metalorganic chemical vapor deposition). Trimethylgallium is used as the Gasource gas and ammonia is added to supply nitrogen atoms. Hydrogen isalso added in order to dilute the gas and to gasify Ga or N atoms ifthey are located in unstable sites on the lattice. A multiple layeredsemiconductor structure is made by n-doping with Si on the sapphirefollowed by p-doping with Mg to form a junction. Quantum wells andintrinsic layers can be introduced between the p-doped layer and then-doped layer.

The top surface of the p-doped layer is cosputtered with graphite and Agto form a reflective layer. The graphite acts to reduce the CTE of thereflective layer. In this case, the CTE can be graded by controllingAg/C ratio. Ag coating is then resumed without graphite. The Ag layer isthen thickened by electroplating with Cu or Ag.

Example 3

A 2 inch sapphire wafer is deposited with epitaxial GaN by MOCVD (metalorganic chemical vapor deposition). Trimethylgallium is used as the Gasource gas and ammonia is added to supply nitrogen atoms. Hydrogen isalso added in order to dilute the gas and to gasify Ga or N atoms ifthey are located in unstable sites on the lattice. A multiple layeredsemiconductor structure is made by n-doping with Si on the sapphirefollowed by p-doping with Mg to form a junction. Quantum wells andintrinsic layers can be introduced between the p-doped layer and then-doped layer.

The top surface of the p-doped layer is cosputtered with graphite and Agto form a reflective layer. The graphite acts to reduce the CTE of thereflective layer. In this case, the CTE can be graded by controllingAg/C ratio. Ag coating is then resumed without graphite. A monolayer ofmicron diamond particles is spread across the Ag layer, and a Cu layeris electroplated there upon to incorporate the diamond particles. Thediamond particle monolayer functions to further reduce the CTE mismatchand increase of thermal conductivity.

Example 4

A 2 inch sapphire wafer is deposited with epitaxial GaN by MOCVD (metalorganic chemical vapor deposition). Trimethylgallium is used as the Gasource gas and ammonia is added to supply nitrogen atoms. Hydrogen isalso added in order to dilute the gas and to gasify Ga or N atoms ifthey are located in unstable sites on the lattice. A multiple layeredsemiconductor structure is made by n-doping with Si on the sapphirefollowed by p-doping with Mg to form a junction. Quantum wells andintrinsic layers can be introduced between the p-doped layer and then-doped layer.

The top surface of the p-doped layer is sputtered with a reflectivelayer of Ag to a thickness of about 200 nm. A Cu metal layer issputtered onto the Ag layer. A monolayer of micron diamond particles isspread across the sputtered Cu layer, and the Cu layer is thickened byelectroplating to incorporate the diamond particles to reduce the CTEmismatch and increase of thermal conductivity.

Example 5

An LED wafer with GaN on sapphire is metalized with a gold layer. Anethanol-diluted wax layer is spread across the top of the gold layer.Diamond particles of about 150 μm in size are pressed across the layer,and excess diamond particles not adhered to the layer are removed. Thewafer is used as a cathode and is immersed in a liquid electrolyte withcopper as the anode, and the wafer is electroplated to cover the diamondparticles in-situ with copper. The sapphire layer is split by laserirradiation and removed, and the exposed GaN surface is coated with anITO electrode except for a small area where gold is coated as an anode.The copper layer is used as the cathode. Thus vertical stack LED is madewith electrodes on the opposing sides.

Example 6

An LED wafer having multiple layers of doped GaN on sapphire issputtered with a reflector layer of Ag, and then a nucleation enhancerlayer of Ti. An electrically conductive amorphous diamond layer is thendeposited on the Ti layer by cathodic arc. The amorphous diamond ismetalized by sputtering with Cr followed by Cu. The Cu layer isthickened by conventional electroplating, resulting in copper bondedGaN.

Example 7

A 2 inch sapphire wafer is deposited with epitaxial GaN by MOCVD.Trimethylgallium is used as the Ga source gas and ammonia is added tosupply nitrogen atoms. Hydrogen is also added in order to dilute the gasand to gasify Ga or N atoms if they are located in unstable sites on thelattice. A multiple layered semiconductor structure is made by n-dopingwith Si on the sapphire followed by p-doping with Mg to form a junction.Quantum wells and intrinsic layers can be introduced between the p-dopedlayer and the n-doped layer. The top surface of the p-doped layer issputtered with a reflective layer of Ag to a thickness of about 200 nm.The reflective layer is then sputtered with a nucleation enhancing layerof Ti to about 50 nm thick.

Subsequently, amorphous diamond is deposited on the nucleation enhancinglayer to a thickness of about 1 μm by cathodic arc deposition. Anadditional nucleation enhancing layer of Ti is sputtered on theamorphous diamond layer to a thickness of about 50 nm, followed bysputtering of a Cu metal layer. The device is then removed from thedeposition chamber and immersed in an electrolyte solution including Niand diamond particles for Ni-diamond layer coating by electroplating.The diamond content is about 30 Vol %. A region of the GaN layer is thenlaser irradiated to separate the sapphire wafer from the GaN layer. Thenewly exposed n-doped GaN surface is then sputtered with Au as electrodeat one corner. This will form a vertical stack LED with top and bottomelectrodes.

Of course, it is to be understood that the above-described arrangementsare only illustrative of the application of the principles of thepresent invention. Numerous modifications and alternative arrangementsmay be devised by those skilled in the art without departing from thespirit and scope of the present invention and the appended claims areintended to cover such modifications and arrangements. Thus, while thepresent invention has been described above with particularity and detailin connection with what is presently deemed to be the most practical andpreferred embodiments of the invention, it will be apparent to those ofordinary skill in the art that numerous modifications, including, butnot limited to, variations in size, materials, shape, form, function andmanner of operation, assembly and use may be made without departing fromthe principles and concepts set forth herein.

What is claimed is:
 1. A method for fabricating a vertical lightemitting diode, comprising: providing a substrate; forming asemiconductive layer on the substrate, the semiconductive layerincluding a compound made of elements selected from Group II elements toGroup VI elements; forming a metallic reflective layer coupled to thesemiconductive layer; forming at least one interlayer and at least onediamond-like carbon layer coupled to the metallic reflective layer;forming a composite material layer coupled to the diamond-like carbonlayer; removing the substrate; forming a first electrode layer and asecond electrode layer on a side of the semiconductive layer and a sideof the composite material layer respectively and; forming a transparentdiamond-like carbon layer is formed on one side of the semiconductivelayer opposite to the diamond-like carbon layer.
 2. The method of claim1, wherein the at least one interlayer and the at least one diamond-likecarbon layer are substantially interstacked at one side of the metallicreflective layer.
 3. The method of claim 1, further comprising polishingthe composite material layer to about Ra<1 μm.
 4. The method as claimedin claim 1, wherein the transparent diamond like carbon layer includeshydrogen atoms therein, wherein the content of the hydrogen atoms isfrom about 15 at % to about 40 at % based on the total amount of thetransparent diamond-like carbon layer.
 5. The method as claimed in claim1, wherein the composite material layer is connected with the metallicreflective layer by soldering using Au or Au—Sn at about 300° C. or by ahigh temperature connecting method.
 6. A vertical light emitting diode,comprising: a semiconductive layer including a compound made of elementsselected from Group II elements to Group VI elements; a metallicreflective layer coupled to the semiconductive layer; at least oneinterlayer; at least one diamond-like carbon layer, wherein the at leastone interlayer and the at least one diamond-like carbon layer areinterstacked at one side of the metallic reflective layer opposite thesemiconductive layer; a composite material layer coupled to thediamond-like carbon layer; a first electrode layer and a secondelectrode layer located on a side of the semiconductive layer and a sideof the composite material layer respectively and; a transparent diamondlike carbon layer located on one side of the semiconductive layeropposite the diamond-like carbon layer.
 7. The vertical light emittingdiode of claim 6, wherein the composition of the semiconductive layer isselected from the group consisting of Al2O3, Si, SiC, GaAs, GaP, AlP,GaN, graphite, hBN, diamond or a combination thereof, or selected fromthe group consisting of a nitride, a phosphide, or an arsenide includingat least one cation selected from B, Al, Ga, In, Be, or Mg.
 8. Thevertical light emitting diode of claim 6, wherein the metallicreflective layer includes at least one material selected from the groupconsisting of Ag, Al, Ni, Co, Pd, Pt, Au, Zn, Sn, Sb, Pb, Cu, CuAg,NiAg, and alloys thereof.
 9. The vertical light emitting diode of claim6, wherein the thickness of the metallic reflective layer is from about100 nm to about 500 nm.
 10. The vertical light emitting diode of claim6, wherein the interlayer includes at least one material selected fromthe group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, and alloysthereof.
 11. The vertical light emitting diode of claim 6, wherein thethickness of the interlayer is from about 50 nm to about 500 nm.
 12. Thevertical light emitting diode of claim 6, wherein the composite materiallayer comprises a composite material composed of at least one metal anddiamond, in which the diamond is substantially arranged in a form ofsingle layer or multi-layers, or the diamond is randomly distributed inthe composite material.
 13. The vertical light emitting diode of claim12, wherein the diamond content in the composite material is from about25 wt % to about 60 wt %.
 14. The vertical light emitting diode of claim13, wherein the metal includes at least one material selected from thegroup consisted of Cu, Ag, Co, Ni, W, Fe, Ti, Cr, and B.
 15. Thevertical light emitting diode of claim 6, wherein the composite materiallayer has a thickness of from about 100 μm to about 500 μm.
 16. Thevertical light emitting diode of claim 6, wherein the composite materiallayer has a thermal expansion coefficient of from about 2 ppm/° C. toabout 10 ppm/° C.
 17. The vertical light emitting diode of claim 6,wherein the transparent diamond like carbon layer comprises hydrogenatoms therein, wherein the content of the hydrogen atoms is from about15 at % to about 40 at % based on the total amount of the transparentdiamond like carbon layer.